Centrifugal separators used in continuously separating blood components can employ a disposable plastic channel that is fitted within a centrifuge bowl that is rotatably driven by a motor. The channels typically have an inlet for whole blood and two or more outlets at different radial locations to remove separated fractions of blood components in the channels, plasma being at the most radially inward location and red blood cells being at the most radially outward location. In various component collection or exchange procedures the red blood cells are usually returned to the patient/donor along with some other components during the continuous separation procedure.
At the end of a separation procedure, it is desirable to remove the red blood cells remaining in the channel and to return them to the patient/donor. In one prior art centrifuge system involving a plastic separation channel of the general type disclosed in Kellogg et al. U.S. Pat. No. 4,094,461, at the end of a run saline is connected to the input line. A pinch valve blocks the input line while a pump pulls on an output line to cause the channel to collapse, and the pinch valve then unblocks the input line, causing saline to quickly enter the channel and to flush red blood cells out.